The invention relates generally to a control means which allows a single standardized construction for an air handling unit which can be applied to various input line voltages and frequencies. While described as being specifically a motor control for heating, ventilating and air-conditioning air handling equipment, the system has broader application for multi-speed motor control systems which also need satisfy a separate low voltage requirement of the system.
In multi-speed motors designed for use on a worldwide basis, significant problems have arisen when a motor designed for a high-speed operation at 230 V/60 Hz is used in locations where the voltage and frequency vary from the 230 V/60 Hz norm. Other line voltage and frequency conditions encountered are 230 V/50 Hz, 208 V/50 Hz and 208 V/60 Hz.
When such alternate voltage and frequency conditions are encountered, poor motor speed control, high motor temperatures and unstable motor operation often result. Thus, motor life is shortened and performance reduced.
Other systems related to the present invention include extended winding motors, choke coils and auto-transformers. Such systems have proven either to be unstable for various voltage/frequency applications or have required a separate and costly transformer to supply the isolated low voltage needs of a heating and air conditioning system.
Accordingly, it is an object of the invention to provide a combined auto-transformer and transformer into a single construction which accomplishes motor speed control and which supplies a needed separate low voltage for a system.
It is a further object of the invention to provide a combined auto-transformer and transformer system wherein the auto-transformer is specially wired to accommodate the various voltages and frequencies encountered on a worldwide basis and still allow accurate, stable motor speed control without motor overheating.
It is a further object to provide that such combined auto-transformer and transformer system be utilized in conjunction with a line voltage terminal block in such manner that the unit may be easily field wired for any encountered voltage and frequency thus permitting efficient blower motor operation on a worldwide basis while using a single standardized motor design to reduce unit costs.
It is a still further object of the invention to incorporate the combined auto-transformer and transformer design into a high, medium and low blower motor speed system with stable motor operation at all speeds.
It is a further object to provide a combined auto-transformer and transformer system wherein the auto-transformer has specially designed tapping locations to allow variations on motor speeds if desired by the user.
These and further objects and advantages of the present invention will become apparent as the following description proceeds, and the features of novelty characterizing the invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.